Electrical contact apparatus



w. G. BRADLEY ETAL 1 2,915,731

ELECTRICAL CONTACT APPARATUS Dec. 1, 1959 2 Sheets-Sheet 2 Filed April1, 1957 may mud m mam 5 M W 0 0 w A n n Mm W United States PatentELECTRICAL CONTACT APPARATUS William G. Bradley, Memphis, Tenn., andFrank D.

Patrick, Freeport, Tex., assignors to The Dow Chemical Company, Midland,Mich., a corporation of Delaware Application April 1,1957, Serial No.649,948

4 Claims. (Cl. 339- This invention relates to apparatus for stabilizingthe electrical resistance between a fixed electrical contact and arotatable contact which operates at high radial velocity.

When electrical contact is to be made between a rotating member, such asa shaft, and a fixed electrical contact, two types of wiper contacts arecommonly used.

high velocities, or the brush makes only intermittent con tact with therotating member. In the mercury type contact described above, as theradial velocity of the rotating contact arm increases the mercury tendsto vortex and the electrical contact between the arm and mercury isinterrupted. Y. r

In some current and potential measuring applications, especiallylaboratory type measurements, the use of electrical contacts of theabove described types introduces considerable error.

Accordingly, a principal object of this invention is to provide improvedelectrical contact apparatus of the type in which a fixed electrode iscoupled to a moving electrode and which exhibits low electrical noise,low resistance and no current interruption while the apparatus isoperated.

In accordance with this invention, apparatus is provided for directing astream of electrically conductive fluid (connected to a fixed electrode)against a moving electrode to maintain positive electrical contacttherebetween,

The invention, as Well as additional objects and advantages thereof,will best be understood when the following detailed description is readin connection with the accompanying drawings, in which:

Fig. 1 is a side elevational view, partly in section of electricalcontact apparatus in accordance with this invention;

Fig. 2 is a sectional view taken along the line 2--2 of Fig. 1;

Fig. 3 is a sectional view taken along the line 3--3 of Fig. 1, and

Fig. 4 is a sectional view taken along the line 4-4 of Fig. 1.

Referring to the drawing, there is shown a rotatable shaft supported ina vertical position on a suitable journal and thrust bearing assembly,indicated generally by the numeral 12. A somewhat cup-shaped member,indicated generally by the numeral 14, is secured to the upper end 16 ofthe shaft 10 by any suitable means such as the set screw 18. Thecup-shaped member 14 has a 2,915,731 Patented Dec. 1, 1959 side wall 20which is cylindrically shaped and which has an inner diameter which issomewhat larger than the diameter of the shaft 10. The side wall 20 andshaft 10 are coaxially disposed with respect to one another. The brim orflanged part 22 at the lower part of the cup-shaped member 14, whenviewed in transverse crosssection, defines an acute angle with respectto the side wall 20. The flanged part 22 may, however, be disposedbetween the ends of the side wall 20 if desired.

The upper part of the shaft 10 and the cup-shaped member 14 aresurrounded by a box-like structure, indicated generally by the numeral24, which has an upper compartment 26, and a lower compartment 28', thecompartments being separated by a common partition 30. A hollowcylindrical member 32 extends upwardly from .the base 33 of the box-likeenclosure 24, passing through the partition 30 (and sealed with respectthereto) and extending between the shaft 10 and the side wall 20 of thecup-shaped member 14.

A hollow cylindrical member 34 which is larger in diameter than thediameter of the side wall 20 of the cup-shaped member 14 extends throughthe removable top 36 of the enclosure 24 and telescopes over the cup- 34are telescoped within one another over a part of their length and arecoaxial with respect to the shaft 10 and cup-shaped member 14.

A pair of conduit members 42', 44, disposed on diametrically oppositesides of the cup-shaped member 14, extend from near the brim or flangepart 22 of the cupshaped member 14 through the partition 40 andcommunicate with the upper compartment 41 of the cylindrical member 34.The conduit members 42, 44 are disposed between and are substantiallyparallel with the side wall 20 of the cup-shaped member 14 and thecylindrical member 34. The output end of the members 42, 44 are close toand directed toward the flange 22.

An overflow conduit 46 is coupled between the upper compartment 41 andthe lower compartment 28 of the enclosure 24. A fluid return line 48 iscoupled, through a pump 50, from the bottom of the compartment 28 to theupper part of the upper compartment 41. shown, the line 48 is coupled tothe upper compartment 41 through the top or closure section 52 of thecylindrical member 34. A vent 54 and a fixed or non-rotatable electrode56 also extends through the top or closure section 52, the lower end 58of the electrode 56 being near to the partition 40 and in any event isbelow the fluid level of the compartment 41.

In operation mercury (or other electrically conductive metal or alloywhich melts at low temperatures, such as Woods metal, bismuth-tinalloys, or lead, for example) is placed in the upper compartment 41 ofthe cylindrical member 34. The electrically conductive metal 60,referred to hereafter as mercury, flows through the tubes or conduits42, 44 and impinges as a continuous stream on the flange 22 of the cupshaped member 14. The rotation of the shaft 10 causes the mercury to bethrown, by centrifugal force, from the flange 22 and onto the side 62 orbottom partition 30 of the compartment 26.

The upper part of the partition 30 slopes downwardly, in a steppedmanner, from the outer part to the inner part thereof. Fluid drainagebores 64, 66, extend through the partition 30 to permit mercury to passthrough the partition 30 and fall into the lower compartment 28 fromwhence it is pumped through the tube or line 48 into the uppercompartment 41 of cylindrical member 34.

A bore 72 extends through the partition 3%? from the side wall 62 of theenclosure 24, communicating with the compartment 28. A tube '74, coupledto the bore 72, may be connected, if desired, with a vacuum pump 76, toforce air between the shaft 10, cylindrical member 32, down between thecylindrical member 32 and the wall 20 of the cup shaped member 14 andout through the partition 30, thus preventing a buildup of mercury alongthe space between the inner part of the wall 20 of the cup shaped member14 and the wall of the cylindrical member 32.

Thus, with the fixed or non-rotatable electrode 56 making constantcontact with the pool of mercury 60a, the continuous stream of mercurywhich impinges on the flange 22 of the rotating cup shaped member 14assures a continuous low resistance, low noise level electrical contactwith the rotating shaft 10 to which the cup-shaped member is secured.The pump 50 continually replenishes the mercury from the pool 60 incompartment 28 to the pool 60a in the upper compartment 41.

In one mercury brush type apparatus constructed in accordance with thisinvention the electrode 56 is made of carbon or wetted steel rod. Theflange 22 of the cup shaped member 14 must also be wetted, that is,freed of oxide film and amalgamated with mercury. The shaft 10 and cupshaped member are made of stainless steel and the enclosure 24,cylindrical member 32 and cylindrical member 34, plus partitions 30 and40 are made of a plastic material such as Plexiglas. The mercurypressure head is between 6 and 8 inches with tubes 42, 44 having aninner diameter of about inch. However, other materials of constructionand enclosure configurations than those illustrated may be adapted tousage in making mercury (or other electrically conductive flowablematerials) brush contacts without departing from the scope of thisinvention.

We claim:

1. Apparatus for making continuous, substantially constan-t resistanceelectrical contact between a non-rotatable electrode and a verticallydisposed met al shaft-like rotatable electrode having an upper end,comprising an inverted cup shaped metal member having a rim and being oflarger internal diameter than the diameter of said rotatable electrode,said cup shaped member having an out wardly extending flanged partdisposed adjacent to said rim, the cup shaped member being coaxiallydisposed rim downwardly over the upper end of said shaft and securedthereto, an upper reservoir of electrically conductive flowablematerial, the non-rotatable electrode extending into said flowablematerial, said upper reservoir being disposed above the upper end ofsaid rotatable electrode, at least one tubular member having an upperend and a lower end, said upper end communicating with said upperreservoir and said lower end being close to and directed towards the rimon said inverted cup-shaped member, a lower reservoir, enclosure meansfor directing said flowable material which leaves said flange into saidlower reservoir, and means including a pump and conduit for pumping saidconductive flowable material from said lower reservoir to said upperreservoir.

2. Apparatus in accordance with claim 1, wherein an overflow conduit isconnected between said upper reservoir and said lower reservoir.

3. Apparatus in accordance with claim 1, wherein a tubular wall extendsthrough said lower reservoir and between said rotatable electrode andsaid inverted cupshaped member.

4. Apparatus in accordance with claim 1, wherein a tubular sectionextends downwardly from said upper reservoir and telescope over saidinverted cup shaped member.

References Cited in the file of this patent UNITED STATES PATENTS2,044,180 Newton June 16, 1936

